Method and system for identifying radio frequency identification (RFID) tag location using a switchable coil

ABSTRACT

Aspects of a method and system for identifying a radio frequency identification (RFID) tag location using a switchable coil are presented. Aspects of the systems may include one or more processors that enable selection of an inductor coil from a plurality of inductor coils. The selection of the inductor coil may be based on a change in an electromagnetic field, with respect to an initial electromagnetic field, as detected by the selected inductor coil. The processors may enable transmission of a signal, having a transmitter frequency in the UHF frequency band, via the selected inductor coil.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application makes reference to:

U.S. application Ser. No. 11/536,678, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,682, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,650, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,644, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,676, filed Sep. 29, 2006:

U.S. application Ser. No. 11/536,659, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,673, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,679, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,670, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,672, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,648, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,669, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,666, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,675, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,685, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,645, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,655, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,660, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,657, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,662, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,688, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,667, filed Sep. 29, 2006;

U.S. application Ser. No. 11/536,651, filed Sep. 29, 2006; and

U.S. application Ser. No. 11/536,656, filed Sep. 29, 2006.

The above stated applications are hereby incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to wireless communication.More specifically, certain embodiments of the invention relate to amethod and system for identifying a radio frequency identification(RFID) tag location using a switchable coil.

BACKGROUND OF THE INVENTION

As portable electronic devices and wireless devices become more popular,an increasing range of mobility applications and services are emerging.There are well established radio broadcast services, utilizing theamplitude modulation (AM) and/or frequency modulation (FM) frequencybands that allow reception of audio information and/or data at an FMreceiver.

Radio frequency identification (RFID) is a data collection technologythat enables the storing and remote retrieval of data utilizing devicesreferred to as RFID tags, or transponders. An RFID transponder maycomprise a silicon integrated circuit, or chip, and an antenna thatenables the RFID transponder to receive and respond to radio frequency(RF) queries from an RFID transceiver, or reader. The RFID transpondermay comprise memory, for example a random access memory (RAM) or anelectrically erasable programmable read only memory (EEPROM), whichenables storage of data. The data may comprise an electronic productcode (EPC) that may be utilized to locate an item to which the RFIDtransponder is attached. For example, libraries may attach RFIDtransponders to books to enable the tracking of books that are checkedout to library patrons. RFID transponders may be integrated intoplastic, credit card sized devices referred to as “smart cards.” TheRFID transponders in smart cards may enable storage of accountinformation that enables the holder of the smart card to purchase goodsand services. The smart card, for example, may store a current balancethat indicates a monetary value of goods and services that may bepurchased with the smart card. The smart card holder may purchase goodsand services by holding the smart card in the proximity of an RFIDtransceiver that retrieves account information from the smart card. TheRFID transceiver may, for example, decrease the current balance toreflect purchases and store the updated value in the smart card. TheRFID transceiver may also increase the current balance when the userpurchases additional monetary value.

Two of the challenges in the development of radio frequencyidentification (RFID) systems are the inexorable quest to reduce thecost and size of RFID transponder circuits, and the need to providesecure communications environment between communicating RFID systems.However, requirements associated with the design and implementation ofpassive components may limit the ability to reduce the cost and size ofRFID transponder circuits in RFID systems. For example, antennas and/orcoupling coils, utilized to enable reception of signals at the RFIDtransponder circuit, may be too large and bulky to integrate on the sameintegrated circuit chip with the RFID transponder circuit. Furthermore,circuitry that may enable secure communications based on the use ofvarious data encryption algorithms may require levels of operating powerconsumption that are not practical for implementation in RFID systems.

Near field communication (NFC) is a communication standard that enableswireless communication devices, such as cellular telephones,SmartPhones, and personal digital assistants (PDAs) to establishpeer-to-peer (P2P) networks. NFC may enable electronic devices toexchange data and/or initiate applications automatically when they arebrought in close proximity, for example ranging from touching, or 0 cm,to a distance of about 20 cm.

NFC may enable downloading of images stored in a digital camera, to apersonal computer, or downloading of audio and/or video entertainment toMP3 devices, or downloading of data stored in a SmartPhone to a personalcomputer, or other wireless device, for example. NFC may be compatiblewith smart card technologies and may also be utilized to enable purchaseof goods and services.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF SUMMARY OF THE INVENTION

A method and system for identifying a radio frequency identification(RFID) tag location using a switchable coil, substantially as shown inand/or described in connection with at least one of the figures, as setforth more completely in the claims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary near field UHF RFID system, inaccordance with an embodiment of the invention.

FIG. 2 is diagram of exemplary inductor coil switching circuitry, inaccordance with an embodiment of the invention.

FIG. 3 is a diagram of an exemplary power amplifier circuit comprising aplurality of switchable inductor coils, in accordance with an embodimentof the invention.

FIG. 4 is a flow chart illustrating exemplary steps for identifying anRFID transponder location utilizing switchable inductor coils, inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor identifying a radio frequency identification (RFID) tag locationusing a switchable coil. In various embodiments of the invention, anRFID reader may select a current inductor coil from a plurality ofinductor coils, which may be utilized for transmitting and/or receivingnear field RFID signals having a frequency in the ultra high frequency(UHF) band. An exemplary UHF frequency band may comprise a range offrequencies from about 300 MHz to about 3 GHz. In an exemplaryembodiment of the invention, the RFID signals may have a frequency ofabout 900 MHz. In various embodiments of the invention, RFID systems maycommunicate based on near field communications (NFC).

The RFID reader may utilize the selected inductor coil to detect themagnitude and/or direction of an electromagnetic field in the immediatevicinity of the RFID reader to determine whether an RFID transponder islocated within the immediate vicinity of the RFID reader. If an RFIDtransponder is located, the RFID reader may utilize the current inductorcoil to initiate a near field RFID communication with the RFIDtransponder. If an RFID transponder is not located, the RFID reader mayselect a subsequent inductor coil from the plurality of inductor coils,and attempt to locate an RFID reader by utilizing a method substantiallysimilar to that described above. Accordingly, switching among aplurality of coil increases that probability that a coil in theimmediate vicinity of the RFID reader may be detected.

FIG. 1 is a block diagram of an exemplary near field UHF RFID system, inaccordance with an embodiment of the invention. Referring to FIG. 1,there is shown an RFID reader 102, and a single chip RFID transpondercircuit 120. The RFID reader 102 may comprise a power amplifier 104, aprocessor 106, a local oscillator 108, and memory 110. The poweramplifier 104 may comprise an amplitude modulator 112, a plurality ofcurrent sources 114 a, 114 b, . . . , and 114 c, a plurality oftransistors 116 a, and 116 b, and an inductor 118. The single chip RFIDtransponder circuit 120 may comprise an RFID transponder block 122, andan inductor coil 124. The inductor coil 124 may comprise at least onecapacitor 126, and at least one inductor 128.

The RFID reader 102 may comprise suitable logic, circuitry, and/or codethat may enable generation and transmission of data via an RFID signalhaving a frequency within the UHF frequency band. The RFID reader 102may enable the data to be represented as symbols, where the symbols maybe transmitted via the RFID signal. A symbol may comprise a group ofdata bits. The RFID reader 102 may generate the symbol by generating acurrent, the magnitude of which may be proportional to the magnitude ofa binary word formed each the group of bits. The symbol may be modulatedbased on a local oscillator signal having a frequency that may beapproximately equal to the frequency of the corresponding transmittedRFID signal. The RFID reader 102 may transmit the data via the RFIDsignal by generating an electromagnetic field, the magnitude and/ordirection of which may vary based on the portion of the data containedwithin each transmitted symbol.

The RFID reader 102 may receive data via a received RFID signal bydetecting variations in the magnitude and/or direction of anelectromagnetic field in the immediate vicinity of the RFID reader 102.Based on the detected variations within the electromagnetic field, theRFID reader 102 may generate a current signal, the magnitude of whichmay vary with time based on the magnitude and/or direction of theelectromagnetic field at corresponding time instants. The RFID reader102 may demodulate the current signal based on the local oscillatorsignal to generate a plurality of received symbols. Based on themagnitude of each received symbol, the RFID reader 102 may detect one ormore bits contained in the received data.

The processor 106 may comprise suitable logic, circuitry, and/or codethat may enable generation of data to be transmitted of RFID signalsand/or processing of data contained in received RFID signals. Theprocessor 106 may generate groups of bits that may be utilized to formsymbols, where the symbols may be utilized to generate transmitted RFIDsignals. The processor 106 may also enable selection of transmittingfrequencies that may be utilized to generate RFID signals. The processor106 may enable detection of bits from received RFID signals.

The local oscillator 108 may comprise suitable logic, circuitry, and/orcode that may enable generation of a local oscillator signal. The localoscillator signal may be utilized to modulate data that may betransmitted via RFID signals. The local oscillator 108 may enablegeneration of RFID signals having a frequency in the UHF frequency band.In an exemplary embodiment of the invention, the local oscillator 108may enable generation of signals having a frequency of about 900 MHz.The local oscillator 108 may generate differential local oscillatorsignals LO⁺ and LO⁻.

The memory 110 may comprise suitable logic, circuitry, and/or code thatmay enable storage, and/or retrieval of information, data, and/or code.The memory 110 may enable storage and/or retrieval of data that may bereceived or transmitted by the RFID reader 102 in a near field RFIDcommunication. The memory 110 may comprise a plurality of random accessmemory (RAM) technologies such as, for example, DRAM, and/or nonvolatilememory, for example electrically erasable programmable read only memory(EEPROM).

The power amplifier 104 may enable reception of a group of bits, B₀, B₁,. . . and B_(N), which may be utilized to generate symbols. Each symbolmay comprise a plurality of signal amplitude levels wherein eachamplitude level may correspond to a specific binary combination of bitsB₀, B₁, . . . , and B_(N). The symbols may be modulated, based on alocal oscillator signal, to generate an RFID signal having a frequencywithin the UHF frequency band. The power amplifier 104 may enabletransmission of the RFID signal by inducing variations in the magnitudeand/or direction of an electromagnetic field in the immediate vicinityof the RFID reader 102.

The power amplifier 104 may enable reception of RFID signals bygenerating an electromagnetic field in the immediate vicinity of theRFID reader 102. The power amplifier 104 may enable detection ofvariations in the magnitude and/or direction of the electromagneticfield. Based on the variations in the magnitude and/or direction of theelectromagnetic field, the power amplifier 104 may enable detection ofreceived RFID signals. The power amplifier 104 may detect individualsymbols received via the received RFID signals, from received groups ofbits may be detected. The detection of bits from the received RFIDsignal may enable the RFID reader 102 to receive data from received RFIDsignals.

The amplitude modulator 112 may comprise suitable logic, circuitry,and/or code that may enable control of current flow from a plurality ofcurrent sources 114 a, 114 b, . . . , and 114 c based on a group of bitsB₀, B₁, . . . , and B_(N). The group of bits B₀, B₁, . . . , and B_(N)may be associated with a symbol, where the symbol comprises at least aportion of the data to be transmitted by the power amplifier 104. Forexample, for a bit value B₀=1, the amplitude modulator 112 may enableclosure of a switch controlling the current source 114 a, therebyenabling the current source 114 a to conduct current. By contrast, for abit value B₀=0, the amplitude modulator 112 may enable opening of aswitch controlling the current source 114 a, thereby disabling thecurrent source 114 a to conduct current. As the number of bits for whichthe binary value is 1 increases in a group of bits B₀, B₁, . . . , andB_(N), the total current flow through the plurality of current sources114 a, 114 b, . . . , and 114 c may increase. Consequently, theamplitude associated with the corresponding symbol may also increase. Asthe number of bits for which the binary value is 0 increases in a groupof bits B₀, B₁, . . . , and B_(N), the total current flow through theplurality of current sources 114 a, 114 b, . . . , and 114 c maydecrease. Consequently, the amplitude associated with the correspondingsymbol may also decrease. In an exemplary embodiment of the invention,N=7 where N is a variable that may indicate a number of bits in thegroup of bits B₀, B₁, . . . , and B_(N).

The plurality of transistors 116 a, and 116 b may form a differentialamplifier circuit, which receives differential input signals, LO⁺ andLO⁻, from a local oscillator signal. When a differential positivevoltage is applied to the inputs of the transistors 116 a and 116 b, thedifferential input signals may enable current flow through thetransistors 116 a and 116 b. When a differential negative voltage isapplied to the inputs of the transistors 116 a and 116 b, thedifferential input signals may disable current flow through thetransistors 116 a and 116 b. When current flow is enabled through thetransistors 116 a and 116 b, a current may flow through the inductor118, the magnitude is about equal to the magnitude of the aggregatecurrent flow through the plurality of current sources 114 a, 114 b, . .. , and 114 c. When current flow is disabled through the transistors 116a and 116 b, the magnitude of the current flow through the inductor 118may be about 0. In this regard, the differential input signals, LO⁺ andLO⁻, may enable application of a time varying current signal to theinductor 118.

The application of the time varying current signal may enable theinductor 118 to generate an electromagnetic field in the vicinity of thepower amplifier 104. The magnitude and/or direction of theelectromagnetic field may correspondingly vary with respect to time inresponse to variations in the current signal applied to the inductor118. In various embodiments of the invention, the inductor 118 maycomprise one or more inductor coils. Each inductor coil may be realizedcomprising a loop geometry, which may be characterized by a loop radius,r_(loop).

The single chip RFID transponder circuit 120 may comprise suitablelogic, circuitry, and/or code that may enable reception of an RFIDsignal having a frequency within the UHF frequency band. The single chipRFID transponder circuit 120 may generate operating power from thereceived RFID signal. The generated operating power may enable thesingle chip RFID transponder circuit 120 to process the received RFIDsignal. The single chip RFID transponder circuit 120 may detect data inthe received RFID signal. The detected data may comprise a request foraccount identification information stored within the single chip RFIDtransponder circuit 120, for example. Based on this data, the singlechip RFID transponder circuit 120 may generate response data. Theresponse data may comprise the requested account identificationinformation. The single chip RFID transponder circuit 120 may transmit asignal that may be generated by modulating the response data and acarrier signal having a frequency, which may be approximately equal to afrequency of the received RFID signal.

The RFID transponder block 122 may comprise suitable logic, circuitry,and/or code that may enable selection of a frequency for receiving anRFID signal, and generation of operating power from the received RFIDsignal. The RFID transponder block 122 may also enable detection of datain the received RFID signal, and generation of response data. The RFIDtransponder block 122 may enable selection of a frequency fortransmitting an RFID signal. A carrier signal may be generated having afrequency, which may be approximately equal to the selected transmittingfrequency. In one exemplary embodiment of the invention, the carriersignal may be generated having a frequency, which may be approximatelyequal to the frequency of the received RFID signal. The RFID transponderblock 122 may enable generation of a response signal by modulating theresponse data and the carrier signal.

The inductor coil 124 may comprise suitable circuitry that may enablereception and/or transmission of RFID signals having a frequency withinthe UHF frequency band. In an exemplary embodiment of the invention, theinductor coil may enable reception and/or transmission of RFID signalshaving a frequency of about 900 MHz. The inductor coil 124 may berepresented as an equivalent circuit comprising at least one capacitor126 and at least one inductor 128. In various embodiments of theinvention, the capacitor 126 and inductor 128 may form a resonantcircuit for which the resonant frequency may be higher than thefrequency of RFID signals received and/or transmitted by the inductorcoil 124.

In operation, the RFID reader 102 may attempt to determine whether anRFID transponder 120 may be in the immediate vicinity by generatinginitial an electromagnetic field. The initial electromagnetic field maycorrespond to a measured impedance of the wireless medium in theimmediate vicinity of the RFID reader 102, Z_(air). As an RFIDtransponder 120 approaches the immediate vicinity, the impedanceassociated with the RFID transponder 120 may modify the measuredimpedance in the vicinity of the RFID reader 102. Consequently, theapproaching RFID transponder 120 may induce changes in theelectromagnetic field from the initial electromagnetic field. The changemay be observed through variations in the magnitude and/or direction ofthe electromagnetic field induced by the approaching RFID transponder120. Based on these variations, the RFID reader 102 may be able tolocate an RFID transponder 120 in the immediate vicinity of the RFIDreader 102. Upon locating the RFID transponder 120, the RFID reader 102may initiate near field RFID communication. The RFID reader 102 mayinitiate the communication by transmitting data to the RFID transponder120 via one or more RFID signals.

The processor 106 may enable selection of a transmitting frequency, andmay enable configuration of the local oscillator 108 to enablegeneration of differential local oscillator signals LO⁺ and LO⁻ having afrequency within the UHF frequency band. Upon detection of the RFIDtransponder 120, the processor 106 may retrieve data stored in thememory 110. The retrieved data bits may be communicated to the amplitudemodulator 112. The processor 106 may communicate control signals to thepower amplifier 104, which enable the power amplifier 104 to generateRFID signals that may be utilized for transmitting the data bits. Thecurrent applied to the inductor 118 when the power amplifier 104 istransmitting data via an RFID signal may generate an electromagneticfield that is detected by the inductor coil 124 when the single chipRFID transponder circuit 120 is receiving the transmitted RFID signal.The variation in current magnitude within the inductor 118 may induce acorresponding variation in current magnitude in the inductor 128. Thevariation in current magnitude within the inductor 128 may enable theinductor 128 and capacitor 126 to generate a corresponding voltage. Themagnitude of the corresponding voltage may be based on the variation incurrent magnitude induced in the inductor 128. The generated voltage maybe applied to the inputs of the RFID transponder block 122. Based on themagnitude of the generate voltage, the RFID transponder block 122 maydetect a symbol within the received RFID signal, from whichcorresponding bits associated with the symbol may be detected.

The single chip RFID transponder circuit 120 may transmit an RFID signalby generating a signal that controls a switch within the RFIDtransponder block 122. When the switch is opened, the impedance measuredacross the terminals of the RFID transponder block 122 may be referredto as Z_(transponder). In this regard, the impedance of the single chipRFID transponder circuit 120, Z_(open), may have a value that isdetermined by the impedance of the inductor 128, the capacitor 126, andthe impedance Z_(transponder). When the switch is closed, the impedancemeasured across the terminals of the RFID transponder block 122 maycorrespond to a short circuit, for which the impedance may be aboutequal to 0. In this regard, the impedance of the single chip RFIDtransponder circuit 120, Z_(closed), may have a value that may bedetermined by the impedance of the inductor 128, the capacitor 126, andthe short circuit impedance of the RFID transponder block 122. Thesignal, which controls the switch within the RFID transponder block 122may have a frequency about equal to the selected transmitting frequencyfor the RFID signal transmitted by the single chip RFID transpondercircuit 120.

The opening and closing of the switch may enable the RFID transponderblock 122 to modulate response data with a carrier signal to generate anRFID signal that is transmitted to the RFID reader 102. For example,opening of the switch may enable the RFID transponder block 122 totransmit a bit having a binary value of 0, while closing of the switchmay enable the RFID transponder block 122 to transmit a bit having abinary value of 1.

When receiving an RFID signal, the power amplifier 104 may generate acurrent that may be applied to the inductor 118. The applied current maygenerate an electromagnetic field as described above. The magnitudeand/or direction of the electromagnetic field may vary in response tothe impedance of the single chip RFID transponder circuit 120. Thus,changes in the impedance of the single chip RFID transponder circuit 120may induce changes in the magnitude and/or direction of theelectromagnetic field generated by the power amplifier 104. Changes inthe electromagnetic field may induce changes in the current flow throughthe inductor 118. By detecting the changes in the current flow throughthe inductor 118 induced by changes in the impedance of the single chipRFID transponder circuit 120, the power amplifier may detect bitstransmitted by the single chip RFID transponder circuit 120. Forexample, the power amplifier 104 may detect a bit having a binary valueof 1 when the impedance of the single chip RFID transponder 120 may beapproximately equal to Z_(closed). For example, the power amplifier 104may detect a bit having a binary value of 0 when the impedance of thesingle chip RFID transponder 120 may be approximately equal to Z_(open).

In various embodiments of the invention, the ability to generate highercurrent levels across the inductor 118 may enable greater sensitivity atthe RFID reader 102. The greater sensitivity may enable the RFID reader102 to locate an RFID transponder 120 in the immediate vicinity. As thecurrent through the inductor 118 is increased, and the sensitivity ofthe RFID reader 102 correspondingly increases, the RFID reader 102 maybe able to locate RFID transponders 120 for increasing distances betweenthe inductor 118 and the inductor coil 124. As shown in FIG. 1, theinductor 118 may be placed at the output of the power amplifier 104 toenable the generation of high current levels in response to relativelylow supply voltage levels, labeled V_(SS) in FIG. 1. When the voltageamplitude across the terminals of the inductor 118 is about 1V, the rootmean square (RMS) current level through the inductor 118 may be about400 mA.

For an inductor 118 that comprises a single inductor coil characterizedby a loop radius, r_(loop), a maximum distance, d_(max), may be definedbetween the inductor 118 and the inductor coil 124. The maximum distanced_(max) may represent a maximum distance for which an RFID reader 102may locate an RFID transponder 120. In various embodiments of theinvention in which the inductor 118 may comprise a single inductor coil,the maximum distance may be represented as shown in the followingequation:r_(loop)≅√{square root over (2)}·d_(max)  Equation [1]

Under some conditions, however, placing the RFID transponder 120 in theimmediate vicinity of the RFID reader 102 may not be sufficient toenable the RFID reader to locate the RFID transponder 120. When theinductor 118 comprises a single inductor coil, for example, the RFIDreader 102 and RFID transponder 120 may need to be precisely aligned toallow the inductor 118, and the inductor coil 124 to be in sufficientlyclose proximity to enable the RFID reader to locate the RFID transponder120. Some users, however, may not be aware of the precise location ofthe inductor 118 within the RFID reader, and/or the inductor coil 124within the RFID transponder 124.

FIG. 2 is diagram of exemplary inductor coil switching circuitry, inaccordance with an embodiment of the invention. Referring to FIG. 2,there is shown, an amplitude modulator 112, a plurality of currentsources 114 a, 114 b, . . . , and 114 c, a plurality of transistors 116a, 116 b, 204 a, 204 b, 206 a, 206 b, 208 a, and 208 b, and an inductor118. The inductor 118 may comprise a plurality of inductor coils 202 a,202 b, and 202 c. The amplitude modulator 112, plurality of currentsources 114 a, 114 b, . . . , and 114 c, and plurality of transistors116 a, and 116 b were previously described in regard to FIG. 1.

FIG. 2 shows an inductor 118, which comprises 3 inductor coils 202 a,202 b, and 202 c. Each of the inductor coils 202 a, 202 b, and 202 c maybe characterized by corresponding loop radii r_(loop1), r_(loop2), andr_(loop3), respectively. In an exemplary embodiment of the invention,each of the loop radii may be approximately equal to r_(loop). Each ofthe inductor coils may detect an inductor coil 124 located at a distanced_(max) in accordance with equation [1].

In various embodiments of the invention, the plurality of inductor coils202 a, 202 b, and 202 c may enable an RFID reader 102 to detect an RFIDtransponder 120 over a larger proximate area than may be the case for anRFID reader 102 in which the inductor 118 comprises a single inductorcoil 202 a.

In operation, the processor 106 may enable a RFID reader 102 toimplement a scanning procedure to locate an RFID transponder 120. Thescanning procedure may initiate automatically, or in response to aninput from a user. In one aspect of the scanning procedure, theprocessor 106 may enable selection of an inductor coil from theplurality of inductor coils 202 a, 202 b, and 202 c. The processor 106may select an inductor coil by sending control signals to thetransistors 204 a, 204 b, 206 a, 206 b, 208 a, and 208 b. For example,the processor 106 may select inductor coil 202 a by sending controlsignals, which couple the gate inputs of the transistors 204 a and 204 bto a supply voltage, labeled as V_(DD) in FIG. 2, while coupling thegate inputs of the transistors 206 a, 206 b, 208 a, and 208 b to ground(GND). The power amplifier 104 may apply a current to the selectedinductor coil, for example 202 a. The processor 106 may then attempt todetermine whether an RFID transponder 120 has been detected. If an RFIDtransponder 120 has been detected, the inductor coil 202 a may beutilized to initiate a near field RFID communication.

If an RFID transponder 120 has not been detected, the processor 106 mayenable selection of a different inductor coil from the plurality ofinductor coils 202 a, 202 b, and 202 c. The processor 106 may selectinductor coil 202 b. The processor 106 may select inductor coil 202 b bysending control signals, which couple the gate inputs of the transistors208 a and 208 b to a supply voltage, labeled as V_(DD) in FIG. 2, whilecoupling the gate inputs of the transistors 204 a, 204 b, 206 a, and 206b to ground (GND). The processor 106 may again attempt to determinewhether an RFID transponder 120 has been detected. If an RFIDtransponder 120 has been detected, the inductor coil 202 b may beutilized to initiate a near field RFID communication.

If an RFID transponder 120 has not been detected, the processor 106 mayselect inductor coil 202 c. The processor 106 may select inductor coil202 c by sending control signals, which may couple the gate inputs ofthe transistors 206 a and 206 b to a supply voltage, labeled as V_(DD)in FIG. 2, while coupling the gate inputs of the transistors 204 a, 204b, 208 a, and 208 b to ground (GND). The processor 106 may again attemptto determine whether an RFID transponder 120 has been detected. If anRFID transponder 120 has been detected, the inductor coil 202 c may beutilized to initiate a near field RFID communication.

Various embodiments of the invention do not impose limitations on theorder in which inductor coils may be selected, or on the number ofattempts that may be made to locate an RFID transponder utilizing agiven inductor coil. For example, in one exemplary embodiment of theinvention, inductor coils may be selected in a round robin fashion, inwhich a different inductor coil is utilized for each attempt to locatean RFID transponder 120 in a first iteration. If an RFID transponder 120has not be located after each of the inductor coils has been utilized,the procedure may halt until a user of the RFID reader 102 undertakes anaction that causes the RFID reader 102 to repeat the procedure in asecond iteration. In a second iteration, inductor coils may be selectedin the same order, or in a different order in comparison to the firstiteration.

In another exemplary embodiment of the invention, inductor coils mayalso be selected in a round robin fashion in a first iteration. Aftereach of the inductor coils has been utilized with no RFID transponder120 being located, a second iteration may begin in which each of theinductor coils may be selected in the same order as in the firstiteration. The RFID reader 102 may continue iterations in a similarfashion until an RFID transponder 102 is located, or until a user of theRFID reader 102 undertakes an action to halt the procedure. In asubsequent iteration, inductor coils may be selected in the same order,or in a different order in comparison to the preceding iteration.

In another exemplary embodiment of the invention, inductor coils may beselected in a non-round robin fashion, for example in random order. Inthis case, a given inductor coil may be reselected before each of theother inductor coils has been selected once since the preceding instancewith the inductor coil was selected. In an exemplary non-round robinsequent, inductor coil 202 a may be selected, followed by selection ofinductor coil 202 b, followed by reselection of inductor coil 202 a,followed by selection of inductor coil 202 c. In another exemplaryembodiment of the invention, a user may manually select an inductor coilthat may be utilized in an attempt to locate an RFID transponder 120.

FIG. 3 is a diagram of an exemplary power amplifier circuit comprising aplurality of switchable inductor coils, in accordance with an embodimentof the invention. Referring to FIG. 3, there is shown a power amplifier104. The power amplifier 104 may comprise a plurality of inductor coils202 a, and 202 b, for example. The power amplifier 104 may comprise aphysical length dimension of about 1,080 μm, and a physical widthdimension of about 955 μm. The chip area may be about 1.03 mm². In anexemplary embodiment of the invention, the power amplifier 104 may befabricated utilizing a 0.18 μm CMOS manufacturing process. In anexemplary embodiment of the invention, the power amplifier 104 may befabricated on a printed circuit board (PCB).

FIG. 4 is a flow chart illustrating exemplary steps for identifying anRFID transponder location utilizing switchable inductor coils, inaccordance with an embodiment of the invention. Referring to FIG. 4, instep 402, a processor 106 may initiate a scan to detect RFIDtransponders 120 in the immediate vicinity of an RFID reader 102. Instep 404, the processor 106 may select a first inductor coil loop 202 a,for example. Step 406 may determine whether an RFID transponder 120 hasbeen detected utilizing the selected inductor coil. If an RFIDtransponder 120 has been located, in step 408, the RFID reader 102 mayinitiate a near field RFID communication with the located RFIDtransponder 120. If an RFID transponder 120 has not been located, instep 410, the processor 106 may select a next inductor coil loop 202 b,for example. Step 406 may follow step 410.

Aspects of a system for identifying a radio frequency identification(RFID) tag location using a switchable coil may comprise one or moreprocessors 106 that enable selection of an inductor coil from aplurality of inductor coils 202 a, 202 b, and 202 c. The selection ofthe inductor coil may be based on a change in an electromagnetic field,with respect to an initial electromagnetic field, as detected by theselected inductor coil. The processors 106 may enable transmission of asignal, having a transmitter frequency in the UHF frequency band, viathe selected inductor coil. The transmitter frequency may be about 900MHz.

The processors 106 may enable generation of the initial electromagneticfield via the selected inductor coil. The processors 106 may also enabledetection of a magnitude and/or a direction of the electromagneticfield, and detection of a magnitude and/or a direction of the initialelectromagnetic field.

The processors 106 may enable detection of the magnitude and/or thedirection of the initial electromagnetic field when an impedance,measured from the selected inductor coil, is approximately equal to animpedance of a wireless communications medium in the immediate vicinityof the selected inductor coil. The processors 106 may enableconfiguration of at least one transistor 204 a to select the selectedinductor coil. The processors 106 may enable transmission of thetransmitted signal via an electromagnetic field generated by theselected inductor coil.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

1. A method for communicating information in a wireless communicationsystem, the method comprising: selecting an inductor coil from aplurality of inductor coils based on a change in an electromagneticfield, with respect to an initial electromagnetic field, detected bysaid selected inductor coil, wherein selecting comprises coupling anon-selected inductor coil, from the plurality of inductor coils, toground; and transmitting a signal, having a transmitter frequency in aradio frequency band, via said selected inductor coil.
 2. The methodaccording to claim 1, wherein said transmitter frequency is about 900MHz.
 3. The method according to claim 1, comprising generating saidinitial electromagnetic field via said selected inductor coil.
 4. Themethod according to claim 1, comprising detecting at least one of: amagnitude and a direction, for said electromagnetic field, and detectingat least one of: a magnitude and a direction for said initialelectromagnetic field.
 5. The method according to claim 4, comprisingdetecting said at least one of: said magnitude and said direction forsaid initial electromagnetic field when an impedance measured from saidselected inductor coil is approximately equal to an impedance of awireless communications medium in an immediate vicinity of said selectedinductor coil.
 6. The method according to claim 1, comprisingconfiguring at least one transistor to select said selected inductorcoil.
 7. The method according to claim 1, comprising transmitting saidtransmitted signal via an electromagnetic field generated by saidselected inductor coil.
 8. A non-transitory computer-readable mediumhaving stored thereon, a computer program having at least one codesection for communicating information in a wireless communicationsystem, the at least one code section being executable by a computer forcausing the computer to perform steps comprising: selecting an inductorcoil from a plurality of inductor coils based on a change in anelectromagnetic field, with respect to an initial electromagnetic field,detected by said selected inductor coil, wherein selecting comprisescoupling a non-selected inductor coil, from the plurality of inductorcoils, to ground; and transmitting a signal, having a transmitterfrequency in a radio frequency band, via said selected inductor coil. 9.The non-transitory computer-readable medium according to claim 8,wherein said transmitter frequency is about 900 MHz.
 10. Thenon-transitory computer-readable medium according to claim 8, whereinsaid at least one code section comprises code for generating saidinitial electromagnetic field via said selected inductor coil.
 11. Thenon-transitory computer-readable medium according to claim 8, whereinsaid at least one code section comprises code for detecting at least oneof: a magnitude and a direction, for said electromagnetic field, anddetecting at least one of: a magnitude and a direction, for said initialelectromagnetic field.
 12. The non-transitory computer-readable mediumaccording to claim 11, comprising detecting said at least one of: saidmagnitude and said direction for said initial electromagnetic field whenan impedance measured from said selected inductor coil is approximatelyequal to an impedance of a wireless communications medium in animmediate vicinity of said selected inductor coil.
 13. Thenon-transitory computer-readable medium according to claim 8, whereinsaid at least one code section comprises code for configuring at leastone transistor to select said selected inductor coil.
 14. Thenon-transitory computer-readable medium according to claim 8, whereinsaid at least one code section comprises code for transmitting saidtransmitted signal via an electromagnetic field generated by saidselected inductor coil.
 15. A system for communicating information in awireless communication system, the system comprising: at least oneprocessor that enables selection of an inductor coil from a plurality ofinductor coils based on a change in an electromagnetic field, withrespect to an initial electromagnetic field, detected by said selectedinductor coil, wherein the selection comprises coupling a non-selectedinductor coil, from the plurality of inductor coils, to ground; and saidat least one processor enables transmission of a signal, having atransmitter frequency in a radio frequency band, via said selectedinductor coil.
 16. The system according to claim 15, wherein saidtransmitter frequency is about 900 MHz.
 17. The system according toclaim 15, wherein said at least one processor enables generation of saidinitial electromagnetic field via said selected inductor coil.
 18. Thesystem according to claim 15, wherein said at least one processorenables detection of at least one of: a magnitude and a direction forsaid electromagnetic field, and detection of at least one of: amagnitude and a direction for said initial electromagnetic field. 19.The system according to claim 18, wherein said at least one processorenables detection of said at least one of: said magnitude and saiddirection for said initial electromagnetic field when an impedancemeasured from said selected inductor coil is approximately equal to animpedance of a wireless communications medium in an immediate vicinityof said selected inductor coil.
 20. The system according to claim 15,wherein said at least one processor enables configuration of at leastone transistor to select said selected inductor coil.
 21. The systemaccording to claim 15, wherein said at least one processor enablestransmission of said transmitted signal via an electromagnetic fieldgenerated by said selected inductor coil.